Image transfer



Nov. 17, 1964 P. w. COVER 3,157,546

IMAGE TRANSFER Filed April 19, 1960 POWDER 23 CLOUD GENERATOR -INVENTOR. PAUL W. COVE R A T TORNE' V United States Patent 3,157,546 IMAGE TRANd'FER Paul W. (lover, Columbus, Ohio, assignor, by mesne assignments, to Xerox Corporation, a corporation of New York Filed Apr. 19, 196i), Ser. No. 23,293 3 Claims. (Ci. 15-231) This invention relates to xerography and more particularly to improved methods and apparatus for transferring Xerographic images.

In the usual form of xerography it is customary to form an electrostatic latent image on the insulating surface of the xerographic plate and then to develop or make visible the latent image through the selective deposition thereon of finely divided electrostatically attractable powder particles. It is generally customary to then transfer the powder image to some other support, such as a sheet of paper, both to achieve better utilization of the image as well as to permit reuse of the Xerographic plate.

Image transfer is a critical step in Xerography, and particularly so in continuous tone xerography. Unusually fine submicron-sizes particles are generally used for continuous tone development, and these are more difficult to transfer than the somewhat larger particles used for development in other forms of Xerography. Yet, in continuous tone xerography, transfer must be very uniform to provide a uniform and pleasing reproduction and must be as complete as possible in order to achieve adequate density in the transferred image and accomplish the production of an accurate copy. A damaged Xerographic plate produces readily detectable image defects when used in continuous tone Xerography. Since plates are reused generally, it is particularly important that the transfer procedures cause a minimum of plate damage. For this reason also, it is desirable that the transfer procedure be 100% effective, since any powder left behind on the plate must be removed by some cleaning procedure which, to some degree, is injurious to the xerographic plate.

In accordance with the present invention, there are now provided improved means and methods whereby continuous tone or other Xerographic powder images can be readily transferred with high quality with 100% efficiency with complete elimination of need for cleaning the xerographic plate before reuse.

It is accordingly the principal object of the present invention to provide improved xerographic image transfer means and methods.

Other objects of the invention and details thereof will be apparent from the subsequent specification, claims and drawing.

The drawing represents a schematic cross-sectional View of an automatic Xerographic machine embodying the invention. The machine includes a cylindrical Xerographic plate 1% which is slowly rotatable about its axis in the indicated direction by a motor or the like (not shown). Plate it bears on its outer surface a layer of insulating material 11 such as a photoconductive insulating layer of vitreous selenium. The support 9 for the selenium layer may comprise aluminum or the like as is known in the art. A corona charging device 12 is positioned to apply a uniform electrostatic charge to plate it). An image projection apparatus including a moving film strip 13, a lens 14 and a lamp 15 projects onto plate it? a pattern of light and shadow of strip 13 which is synchronized in its movement with the linear motion of the surface of plate 10. There is thus formed on insulating layer 11 of plate 19, in accordance with known xerographic principles, a latent electrostatic image corresponding to the projected light image.

Plate 16 then passes in the course of its rotation l atented Nov. 17, 3954 "Ice beneath a development electrode 16 where image development takes place. A powder cloud generator 17 supplies a dispersion of finely divided electrostatically charged powder particles, such as charcoal, to the development electrode and these particles travel along the.

narrow passage provided between the electrode and plate It) and are selectively attracted to the plate. Excess powder particles pass out of the development electrode and are collected by a vacuum cleaner 18. There is thus formed on the surface of plate 10 a powder pattern rep resentative of the light pattern projected on the plate by elements 13, i4 and 15. The methods and apparatus described to this point are completely conventional in the Xerographic art and may be replaced by any of their known equivalents.

Plate ill then passes into contact with the surface of a film forming liquid 19 in pan 20. Liquid 19 wets and penetrates the powder image on plate 10, but does not in any way disturb this pattern. Plate 10 then rotates past and very close to a doctor blade 21 which reduces the liquid film to a uniform, very thin layer. Again, this operation does not disturb the powder image in any way. The film forming liquid 19 then dries to a cohesive film in the course of further rotation of plate 10. The drying time can be reduced through the application of a gentle flow of warm air as shown. A blower 22 provides a supply of air which is forced through heating coils 23 into a plenum chamber 24 from which it is discharged against plate ll After drying, the film forming liquid becomes a cohesive transparent layer in which is imbedded or encapsulated all of the powder image. This layer may be stripped from plate lltl as a self-supporting layer, but it may be rather thin and fragile depending on the film forming material employed and is therefore most conveniently handled in the manner shown. A web of adhesively coated material 25 passing from supply spool 26 to takeup spool 27 is positioned with its adhesively coated face pressed against plate 16 by a soft pressure roller 28. Material 25 may comprise a web of ordinary paper or, for some applications, may be a web of transparent plastic film or the like. It is coated on one side with any of the well known self-adhesive formulations preferably with one having a relatively low degree of tackiness. The layer of dried film forming liquid becomes attached to and adherent upon adhesive material 25 and is removed from plate it with material 25. All of the powder image is accordingly also transferred to material 25 on which it may be viewed. Plate 14), meanwhile, is left in a completely clean condition, free of all powder or other material and may be reused in the Xerographic process without being brushed or otherwise cleaned.

The film forming liquid 19 used in carrying out this invention should be one which dries rapidly to form a clear, thin coherent film which can be readily separated from plate 19 without also pulling olf portions of insulating layer 11 from support 9. The film forming liquid should also have a fairly low viscosity to prevent any disturbance to the powder particles on plate 19. The film forming liquid may harden by solvent evaporation or by chemical reaction, but the former method is generally preferred as being simpler and easier to control. A variety of resinous materials may be used in liquid 19 including plasticized polyvinyl alcohol, cellulose nitrate, polystyrene, and the like. A particularly useful material, and the preferred material, is in approximately 5% solution by weight of cellulose acetate in acetone. When this material is applied to plate 10 and smoothed out by doctor blade 21 to a thickness of from about 10 to about microns, it will dry in about 30 to seconds at room temperature to yield a solid film which can be readily stripped from plate ill without damage to the film or the plate. Thirty to sixty seconds is a short enough drying time to make this transfer process economically practical, but this time can be shortened even further by the useof allow of warm air as shown inthe drawing.

Various other means may be employed to apply film formin liquid 1? to Xerographic plate it). Thus, the liquid may be sprayed, poured, rolled, extruded, or the like.

If the film. is stripped from the plate without a support base attached, it can be fused or attached to a base subsequently. This may be accomplished using a support material having a heat or vapor softenable surface layer such as a polyethylene or microcrystalline wax coating and by applying the support to the stripped film while the coated layer is in a softened condition. For example, this maybe done by rolling the support base against the stripped layer using a heated roller with low pressure and, as should be apparent, such manipulations may be embodied into a device such as that illustrated in the drawing; The benefit of attaching the film to a base is that onecan provide a background color for the image and, of course, make the copy much more durable and less subject to damage during handling.

Although the invention has been shown in conjunction with a continuous automatic machine; it may also be employed in connection with the hand processing of xerographic images. Thus, a flat Xerographic plate with a powderfirnage thereon may be manually dipped in a tank of film forming liquid and allowed to dry, after which the image containing film may be peeled ofi by hand. These and other modifications within the scope of the inventive concept are intended to be encompassed within the appended claims. 7

What is claimed is: 1. The method of transferring an unconsolidated subfmicron sized Xerographic powder image from a temporary support surface to which the powder image is held by electrostatic force comprising applying a low viscosity film forming liquid to said temporary support surface, drawing a doctor blade across said liquid to form a thin layer thereof, causing said layer to dry into a cohesivesolution to from about 10 to about 50 microns, allowing the cellulose acetate solution to dry to a hard cohesive cellulose acetate film having the powder image encapsulated therein, contacting the cellulose acetate film while on said plate with the adhesive surface of anadhesively coated sheet-like transfer material, and removing said transfer material with all or" said powder image from said plate, the cellulose acetate layer and Xerographic powder image being adherent to the transfenmaterial. 7

3. The method of completely transferring an uncon solidated submicron sized Xerographic powder image from a vitreous selenium xerographic plate. to which the powder image is held by electrostatic forces to a permsnent support layer comprising applying a layer of film forming liquid to the selenium plate to wet and penetrate the. powder image, allowing said layer to dry to a cohesive solid layer with the powder image encapsulated therein contacting the cohesive image bearing layer while on said selenium plate with the solid adhesive surface of an adhesively surfaced permanent support layer and removing said permanentsupport layer together with said cohesive layer and all of said powder image from said temporary support surface. 7

References Cite in the file of this patent UNITED STATES PATENTS i 689,320 Markus Dec. 17, 1901 2,212,770 Foster a. Aug. 27, 1940 2,258,958 Kautter et al. July 29, 1941 2,776,907 Carlson 1957 2,784,694 Crurnrine et al. Mar. 12, 1957 2,843,499 Andrus July 15, 19 58 2,895,847

Mayo July 21, 1959 

1. THE METHOD OF TRANSFERRING AN UNCONSOLIDATED SUBMICRON SIZED XERGRAPHIC POWDER IMAGE FROM A TEMPORARY SUPPORT SURFACE TO WHICH THE POWDER IMAGE IS HELD BY ELECTROSTATIC FORCE COMPRISING APPLYING A LOW VISCOSITY FILM FORMING LIQUID TO SAID TEMPROARY SUPPORT SURFACE, DRAWING A DOCTOR BLADE ACROSS SAID LIQUID TO FORM A THIN LAYER THEREOF, CAUSING SAID LAYER TO DRY INTO A COHESIVE FILM AND REMOVING SAID FILM WITH ALL OF THE POWDER IMAGE ENCAPSULATED THEREIN FROM SAID TEMPORARY SUPPORT SURFACE. 